Holyrood's Finance Secretary has called for detailed currency talks with the Treasury, as the debate over the future of the pound in an independent Scotland continued.

John Swinney said the country would not be "shoved about" by the Chancellor, following his latest intervention on the future of Scotland's money, and he accused George Osborne of pre-negotiating "by dictat" on the issue.

Meanwhile, the SNP's political opponents insisted a currency union between an independent Scotland and the rest of the UK would not work and called on First Minister Alex Salmond to set out a back-up plan.

Mr Osborne declared last week that he would not be prepared to enter a currency union with an independent Scotland. Both Labour and the Liberal Democrats have indicated they are also opposed to such a union.

The arrangement is the Scottish Government's preferred plan should Scots vote for independence in September. The SNP administration has already dismissed Mr Osborne's speech as "bluff, bluster and bullying".

Mr Salmond intends to "deconstruct" the Chancellor's position on the issue when he addresses business leaders in Aberdeen tomorrow, arguing that Mr Osborne's stance is "ill-thought-out and misinformed".

Mr Swinney today accused the Chancellor of bluffing, saying he had not addressed "the negative implications for the rest of the United Kingdom of his refusal to go down the route of a currency union".

He told the BBC's Sunday Politics Scotland: "The Chancellor has got to think much more widely about the implications of this issue for the rest of the United Kingdom and come to a sensible and measured position. His contribution on Thursday could in no way have been described as sensible or measured."

He said the Scottish Government's preference for a currency union was in light of expert opinion taken from a range of international economists.

Mr Swinney told the programme: "What I think would be enhanced was if we were to start talking to the Treasury in detail about the arrangements that could take place around the currency zone.

"For the Chancellor to say on the one hand that he will not pre-negotiate and then come to Scotland and essentially pre-negotiate by dictat, is what's caused the very strong reaction in Scotland that the people of this country will not be shoved about by a UK Chancellor. We want have a sensible discussion about all these issues."

But former chancellor Alistair Darling, leader of the pro-Union Better Together campaign, said the idea of a currency union would not "stack up" for Scotland or the rest of the UK.

He told the show: "At the moment we have a single currency, the pound, and it works because we've got a political union, we've got an economic union, we can transfer money around from richer to poorer parts and so on.

"We're being asked to give up that pound and it's now clear a currency union is off the table. What we now need to know is what's the replacement for the pound - something that Alex Salmond either can't or won't tell us."

He said Scots firms would stand to lose more from independence than businesses south of the border.

He added: "We've got just over 200 days before polling day and it is not good enough for... the nationalists, who've been found wanting on Europe and other matters as well, to simply say 'Trust us, we're right, the rest of the world is wrong'. It just isn't credible."

Mr Salmond intends to attack Mr Osborne when he speaks to the pro-independence Business for Scotland organisation.

The First Minister said in advance: "The reality is the pound is as much Scotland's as the rest of the UK. By suggesting otherwise, the Westminster establishment - Tories, Labour and Lib Dems - are reaping a backlash from the ordinary people of Scotland, who feel this is an attempt to bully Scotland ahead of the democratic choice we all look forward to this September.

"I will be deconstructing the Chancellor's ill-thought-out and misinformed intervention point by point, making clear why a currency union not only favours Scotland but is in the clear economic interests of the UK as well."

Writing in today's Sunday Times Scotland, Mr Salmond suggested there was a backlash against the stance taken by the main Westminster parties last week.

"Far from being cowed into submission by the Westminster establishment, it would seem the people are pushing back firmly against an unprecedented attempt to lay down the law to Scotland.

"George Osborne, (shadow chancellor) Ed Balls and (Chief Secretary to the Treasury) Danny Alexander clearly thought their orchestrated efforts of last Thursday would help halt the No campaign's slide in the polls which has seen senior Downing Street strategists deeply worried since the end of last year.

"How little they know or understand the temper of the people of Scotland.

"The indications thus far suggest it is having precisely the opposite effect, with snap polls taken in the immediate aftermath of the Gang of Three's intervention showing two distinct trends. Firstly, that most people will not have their vote in September swayed as a result and secondly, perhaps even more significantly, that among those who say their vote has been affected they are breaking more to Yes as a result."

Meanwhile, a new YouGov poll has found that a majority of the public in England and Wales, 58%, oppose allowing an independent Scotland to continue to use the pound, up 15 points from late November.

When the question was asked towards the end of 2013, people south of the border narrowly opposed a currency union, by 43% against 38% in support.

But now, opposition is at 58% and support is at just 23%, YouGov said.

The 1,868 adults surveyed on Thursday and Friday were asked: "If Scotland did become independent, would you support or oppose an independent Scotland continuing to use the pound as their currency?"

Better Together campaign director Blair McDougall said: "The new poll destroys Alex Salmond's claims over the last few days that people down south would embrace sharing the pound with what would then be a foreign country.

"We now know that if we leave the UK, then we are leaving the pound. If we want to keep the security of the pound, we have to stay in the UK."

Signs of a backlash against the recent unionist interventions appeared with the announcement today that a former Labour member with close political links to Mr Darling now supports the pro-independence Yes Scotland campaign.

Ian Newton, who was Mr Darling's first election agent when he stood for Lothian Regional Council in the 1980s, made the decision in protest at the tactics of the Chancellor and main UK political parties.

In a statement released by Yes Scotland, Mr Newton said: "The manner in which the UK mainstream parties, including Labour, of which I was once a proud member, have dealt with the common currency issues has had a profound effect on me.

"Beforehand, I was what might be described as a passive supporter of independence. Now I want to work for it, and have decided to actively join the Yes Campaign. I also doubt whether I am alone in this reaction."

Blair Jenkins, chief executive of Yes Scotland, said: "This is yet more proof that the threats and bullying attempts by the Westminster government and their Labour allies has backfired. The anger in Scotland is almost tangible."